A semiconductor device such as a LSI (Large Scale Integrated circuit) is manufactured by performing various processes such as an etching process, a CVD (Chemical Vapor Deposition) process, a sputtering process on a semiconductor substrate. A processing method using plasma as an energy source, i.e., a plasma etching process, a plasma CVD process or a plasma sputtering process may be used to perform the etching process, the CVD process or the sputtering process.
Here, a microwave plasma processing apparatus using microwave for generating plasma is described in Japanese Patent Laid-open Publication No. 2006-179477 (Patent Document 1). In Patent Document 1, a dummy load is connected to a cylindrical waveguide positioned between a circular/rectangular waveguide and a circular polarized wave converter. An axis line of this dummy load is deviated from a microwave reflecting body toward the circular polarized wave converter by about ¼ wavelength (L) of a waveguide wavelength of a standing wave reflected from the microwave reflecting body. With this configuration, microwave reflected from a radial waveguide box is effectively absorbed by the dummy load.
Patent Document 1: Japanese Patent Laid-open Publication No. 2006-179477
A conventional plasma processing apparatus described in Patent Document 1 will be briefly explained. FIG. 15 is an enlarged cross sectional view schematically illustrating a part of a conventional plasma processing apparatus. A vertical direction of FIG. 15 corresponds to a vertical direction of the plasma processing apparatus. In FIG. 15, microwaves are also illustrated as images at certain locations.
Referring to FIG. 15, a plasma processing apparatus 101 includes a processing chamber for performing therein a plasma process on a processing target substrate; a circular plate-shaped dielectric plate 102; a thin circular plate-shaped slot antenna plate 103; a circular plate-shaped wavelength shortening plate 104; a microwave generator 105; and a microwave supply unit 106. The dielectric plate 102 transmits microwave into the processing chamber. The slot antenna plate 103 is provided with a multiple number of slot holes (not illustrated) formed through the slot antenna plate 103 in a thickness direction thereof. Further, the slot antenna plate 103 is provided on the dielectric plate 102 and radiates the microwave into the dielectric plate 102. The wavelength shortening plate 104 is provided on the slot antenna plate 103 and transmits the microwave in a radial direction thereof. The microwave generator 105 is disposed outside the processing chamber and generates the microwave. The microwave supply unit 106 is configured to supply the microwave generated by the microwave generator 105 into the processing chamber.
The microwave supply unit 106 includes a vertically elongated coaxial waveguide 107 connected to the slot antenna plate 103. The coaxial waveguide 107 includes a circular rod-shaped inner conductor 108 and an outer conductor 109 disposed outside the inner conductor 108 with a gap 110 therebetween in the radial direction thereof.
In order to generate uniformized plasma under the dielectric plate 102 in a circumferential direction of the dielectric plate 102, the inner conductor 108 of the coaxial waveguide 107 is connected to the slot antenna plate 103 such that a center of the inner conductor 108 in the radial direction aligns with a center of the slot antenna plate 103 in the radial direction. Further, the outer conductor 109 is disposed such that its center in the radial direction coincides with the center of the inner conductor 108 in the radial direction.
In general, in the plasma processing apparatus 101 having the aforementioned configuration, the inner conductor 108 and the outer conductor 109 of the coaxial waveguide 107 are manufactured as separate bodies. Then, the inner conductor 108 and the outer conductor 109 manufactured as separate bodies are combined such that a center of the inner conductor 108 in the radial direction is coincident with a center of the outer conductor 109 in the radial direction. Thereafter, the coaxial waveguide 107 is mounted in the plasma processing apparatus 101 such that the center of the inner conductor 108 in the radial direction aligns with the center of the slot antenna plate 103 in the radial direction. In FIG. 15, a center line indicating the center of the inner conductor 108 in the radial direction is marked by a dashed dotted line 111, and a center line indicating the center of the outer conductor 109 in the radial direction is marked by a dashed double-dotted line 112.
Here, when manufacturing the coaxial waveguide 107, specifically, when combining the inner conductor 108 and the outer conductor 109, the center of the inner conductor 108 in the radial direction and the center of the outer conductor 109 in the radial direction may be deviated from each other. Such a deviation amount is denoted by a length dimension X in FIG. 15. Actually, the deviation amount is about 0.05 mm. For the convenience of understanding, the length dimension X in FIG. 15 is shown as being larger in an exaggerated form than an actual deviation dimension.
If such a deviation is generated, a length of the gap 110 between the inner conductor 108 and the outer conductor 109 in the radial direction becomes non-uniform in a circumferential direction of the coaxial waveguide 107. As a result, intensity of the microwave propagating within the coaxial waveguide 107 also becomes non-uniform in the circumferential direction of the coaxial waveguide 107. Consequently, the intensity of the microwave propagated to the dielectric plate 102 also becomes non-uniform in the circumferential direction thereof, resulting in a non-uniform distribution of an electromagnetic field formed under the dielectric plate 102 in a circumferential direction. Such a non-uniform distribution of the electromagnetic field may cause a non-uniform distribution of plasma generated within the processing chamber in a circumferential direction, resulting in non-uniformity of the plasma process within the surface of the processing target substrate.
Here, when assembling the coaxial waveguide 107, it is very difficult to reduce the deviation between the centers of the inner conductor 108 and the outer conductor 109 so as not to cause the non-uniformity of plasma distribution, and thus, a high equipment cost may be required. Furthermore, the same problems may also be caused when positioning the wavelength shortening plate and the dielectric plate.